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S Beresford

Publications and source records attributed to S Beresford.

7 recordsLinked to original sources
PubMed1999

Explaining community-level variance in group randomized trials.

Between-community variance or community-by-time variance is one of the key factors driving the cost of conducting group randomized trials, which are often very expensive. We investigated empirically whether between-community variance could be reduced by controlling individual- and/or community-level covariates and identified these covariates from four large community-based group randomized trials or surveys: the Working Well Trial; Kaiser Adolescent Survey; Kaiser Adults Survey; and the Eating Patterns Study. We found that adjusting for covariates will often substantially reduce the between-community variance component. Therefore investigators could block the communities according to these covariates, or adjust for these covariates to improve the power of community trials. We found that the community-by-time variance components are always near zero in these data sets, especially for the surveys where a cohort was followed over time. The covariate adjustment had less impact on reducing the community-by-time variance for the cohort samples than for the cross-sectional samples. This suggests that blocking may not be necessary for the design of the group randomized trials where the change from baseline is of primary interest. The Working Well Trial data were used to illustrate this point.

Adolescent↗
PubMed1999

Dietary factors in Parkinson's disease: the role of food groups and specific foods.

PURPOSE: The association between self-reported past food intake and Parkinson's disease (PD) was investigated in a case-control study of men and women aged 40-89 years. METHODS: Newly diagnosed idiopathic PD cases were ascertained from neurologists, and from outpatient and pharmacy computerized databases, at the Group Health Cooperative (GHC) clinics in the Puget Sound region of Washington state. Control subjects were chosen from the GHC patient roster and had no reported history of diagnosed neurodegenerative disease. Dietary data were obtained from structured questionnaires. RESULTS: An increase in PD risk with increasing intake was noted for foods that contain animal fat and foods containing vitamin D. Intake of fruits, vegetables, meats, bread and cereals, or foods containing vitamins A, C, E, or iron was not significantly related to PD risk. Vitamin use, in general, was also not found to be related to PD risk, although a significant trend of increasing risk of PD was noted for intake of vitamin A supplements. CONCLUSIONS: Although these data support previous findings of no association of past intake with most food groups and PD risk, they confirm an increased risk of PD associated with foods containing animal fat.

Adult↗
PubMed1999

Lack of association between duration of breast-feeding or introduction of cow's milk and development of islet autoimmunity.

The hypothesis that early exposure to cow's milk or lack of breast-feeding predisposes to type 1 diabetes remains controversial. We aimed to determine prospectively the relationship of, first, duration of exclusive breast-feeding and total duration of breast-feeding, and second, introduction of cow's milk protein as infant formula, cow's milk, or dairy products, to the development of islet antibodies in early life. Some 317 children with a first-degree relative with type 1 diabetes were followed prospectively from birth for 29 months (4-73). Mothers kept a home diary and answered infant feeding questionnaires at 6-month intervals. No systematic feeding advice was given. Insulin autoantibodies (normal range <5.5%), anti-GAD antibodies (<5.0 U), and anti-IA2 antibodies (<3.0 U) were measured at 6-month intervals. Cox proportional hazards model of survival analysis detected no significant difference between children who did not develop islet antibodies (225 of 317 [71%]), children with one islet antibody raised once (52 of 317 [16.4%]), children with one antibody raised repeatedly (18 of 317 [5.7%]), or children with two or more antibodies raised (22 of 317 [6.9%]), in terms of duration of exclusive breast-feeding, total duration of breast-feeding, or introduction of cow's milk-based infant formulas, cow's milk, or dairy products (relative risk: 0.91-1.09). Four of the children with two or more islet antibodies developed type 1 diabetes. We conclude that there is no prospective association between duration of breast-feeding or introduction of cow's milk and the development of islet autoimmunity in high-risk children.

Aging↗
PubMed1995

Including deaths when measuring health status over time.

Measuring health status over time is problematic when some subjects die, because death does not have a defined value on most health status measures. This situation is different from the usual missing data problem because the health status of the dead is, in a sense, known. We examined eight strategies for incorporating deaths into such analyses using three health status measures taken from two data sets, after which we used computer simulation to explore more fully the effect of deaths. The strategies differed in the amount of influence given to the deaths, varying from none (deaths were discarded) to complete (mortality itself was the health measure). The strategies that gave less influence to deaths tended to show more favorable changes in health over time, and therefore, tended to favor the group that had more deaths. The strategies that were more influenced by death showed more negative changes over time and favored the group with fewer deaths. The choice of strategy should depend on the goals of an intervention. For health promotion studies, we recommend recoding the health variables to estimate the probability that a person will be healthy in 2 years (or in some other period that can be estimated from the data).

Aged↗
PubMed1993

Self-efficacy and health behavior among older adults.

Self-efficacy has a well-established, beneficial effect on health behavior and health status in young and middle-aged adults, but little is known about these relationships in older populations. We examined this issue as part of a randomized trial to determine the cost savings and changes in health-related quality of life associated with the provision and reimbursement of a preventive services package to 2,524 Medicare beneficiaries enrolled in Group Health Cooperative of Puget Sound. Baseline self-efficacy data were collected for all participants in five behavioral areas: exercise, dietary fat intake, weight control, alcohol intake, and smoking. Results reveal that efficacy and outcome expectations for these health behaviors are not independent. Correlational and factor analyses indicate two dimensions of efficacy expectations, one consisting of exercise, dietary fat, and weight control, and another consisting of smoking and alcohol consumption. Outcome expectations of the five behaviors form a single dimension. Older adults with high self-efficacy had lower health risk in all behaviors and better health. Regression analyses detected a positive association between socioeconomic status and health-related quality of life (p < .02), but the strength of the association declined (p < .11) after the self-efficacy measures entered the model, indicating that self-efficacy explains part of the association between socioeconomic status and health status. Interventions aimed at improving self-efficacy also may improve health status.

Age Factors↗
PubMed1991

Participation of higher users in a randomized trial of Medicare reimbursement for preventive services.

In a study of older enrollees in an HMO, we found that seniors who are higher users of health care services are willing to participate in health promotion programs. Although people aged 85 or older and those with chronic diseases are slightly more reluctant to participate, they are willing to make additional visits for health promotion purposes. Close proximity to the clinic and support from their family physician are important correlates of participation.

Age Factors↗